The part I need is the part that has 8 holes and bolts to the worm gear, I think its called a cage, part # AA 4205, one side of mine is cracked and I don't want to weld it.
thanks nick c

All Ford Parts Price Lists shows AA-4205 as the "differential gear case" (2 per truck). The part id was assigned an "AR" suffix even thou it was a production part. This was TT-1028-B (i.e. a TT carryover part). The "AR" suffix assignment is unusual. Most worm drive parts are listed with this suffix. This part is many time cracked.

Well crap - i have 2 halves - one an axle bore into the end and was "fixed" my a large fat washer. That half is cracked. The other half that looks to be great shape I sandblasted it and thought it was good but upon close up inspection has a few tiny micro cracks barely visible to the naked eye on the support ribs...

Heres my theory - noones going to load 5 tons of crap in the back of an AA anymore and drive up a 20* gravel grade. There is an awful lot of meat on those parts even if they are cracked so how hard do we have to worry about them?

Also are you sure with a sandblasted part and a magnifying glass your "good" half isnt also cracked? I find it weird one half would and other half not...the one i thought was good you can just barely see the cracks with the naked eye and i have 20/20 vision...

Last edited by Stakebed on July 25th, 2017, 6:17 am, edited 1 time in total.

The part I need is the part that has 8 holes and bolts to the worm gear, I think its called a cage, part # AA 4205, one side of mine is cracked and I don't want to weld it.
thanks nick c

Nick: think this through. A part that will never be seen, the truck will probably never carry a 'Load" again. ( just parade and grand kid duty). I think I'd weld it up. A lot. make it stronger than it was and use it. Let me know how it goes. I have one hanging on the wall, but would like to keep it. Just in case.